Logos: Difference between revisions

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Logos is a component of the [[Theos]] development suite that allows method hooking code to be written easily and clearly, using a set of special preprocessor directives.
{{soft redirect|https://theos.dev/docs/logos}}

== Overview ==
This article is obsolete, and has been replaced by the [https://theos.dev/docs/logos theos.dev website].

The syntax provided by Logos greatly simplifies the development of MobileSubstrate extensions ("tweaks") which can hook other methods throughout the OS.
If you need historical installation instructions, you can find the last version of this article [https://iphonedev.wiki/index.php?title=Logos&oldid=5734 here].
In this context, "method hooking" refers to a technique used to replace or modify methods of classes found in other applications on the phone.
== Getting Logos ==
Logos is distributed with [[Theos]], and you can use Logos' syntax in any Theos-built project without any extra setup.  For more information about Theos, visit [[Theos|its page]].
== Using Logos ==
=== Examples ===
Write me!
=== List of Logos Directives ===
==== Initialization ====
===== %init =====
<source lang="logos">
%init([<class>=<expr>, …])
%init(Group[, [+|-]<class>=<expr>, …])
Initialize a group (or the default group). Passing no group name will initialize "_ungrouped", and passing class=expr arguments will substitute the given expressions for those classes at initialization time. The + sigil (as in class methods in Objective-C) can be prepended to the classname to substitute an expression for the metaclass. If not specified, the sigil defaults to -, to substitute the class itself. If not specified, the metaclass is derived from the class.
==== Block-level ====
The directives in this category open a block of code which must be closed by an %end directive (shown below).
===== %config =====
<source lang="logos">%config(X=Y);</source>
Set a logos configuration flag.
======Configuration Flags======
* generator
**; MobileSubstrate
**: generate code that uses [[MobileSubstrate]] for hooking.
**; internal
**: generate code that uses only internal Objective-C runtime methods for hooking.
* warnings
**; none
**: suppress all warnings
**; default
**: non-fatal warnings
**; error
**: make all warnings fatal
* dump
**; yaml
**: dump the internal parse tree in YAML format
* patches
**; full
**: when dumping data, include text substitutions for patch points
===== %hook =====
<source lang="logos">%hook Classname</source>
Open a hook block for the class named ''Classname''.
Here's a trivial example:
<source lang="logos">
%hook SBApplicationController
-(void)uninstallApplication:(SBApplication *)application {
    NSLog(@"Hey, we're hooking uninstallApplication:!");
    %orig; // Call the original implementation of this method
===== %subclass =====
<source lang="logos">%subclass Classname: Superclass <Protocol, Protocol></source>
Subclass block - the class is created at runtime and populated with methods. ivars are not yet supported.
===== %group =====
<source lang="logos">%group Groupname</source>
Begin a hook group (for conditional initialization or code organization) with the name ''Groupname''. All ungrouped hooks are in the implicit "_ungrouped" group.
===== %class =====
<source lang="logos">%class Class</source>
Forward-declare a class. Outmoded by %c, but still exists. Creates a $Class variable, and initializes it with the "_ungrouped" group.
===== %new =====
<source lang="logos">%new
Add a new method to a hooked class or subclass. ''signature'' is the Objective-C type encoding for the new method; if it is omitted, one will be generated.
===== %ctor =====
<source lang="logos">%ctor { … }</source>
Generate an anonymous constructor (of default priority).
===== %end =====
<source lang="logos">%end</source>
Close a hook/subclass/group block.
==== Inline ====
===== %c =====
<source lang="logos">%c(Class)</source>
Effectively evaluates to Class, at runtime. Technically, creates $Class and populates it when the "_ungrouped" group is initialized.
===== %orig =====
<source lang="logos">
Call the original hooked method. Doesn't function in a `%new`'d method. Works in subclasses, strangely enough, because MobileSubstrate will generate a supercall closure at hook time. (If the hooked
method doesn't exist in the class we're hooking, it creates a stub that just calls the superclass implementation.) args is passed to the original function - don't include `self` and `_cmd`, Logos does this for you.
===== %log =====
<source lang="logos">%log</source>
Dump the method arguments to syslog.
[[Category:Development Tools]]

Latest revision as of 18:12, 19 February 2022

Soft redirect to:https://theos.dev/docs/logos

This article is obsolete, and has been replaced by the theos.dev website.

If you need historical installation instructions, you can find the last version of this article here.